OK well upon further reflection, it seems the best approach will be to cut-away the damaged wood, such that when I replace the faucet the cylindrical retaining rings sit flat against the underside of the Corian countertop. Seems like a cleaner solution than working-around damaged and swollen wood, which afaict is part of the cabinetry and what I cut-away will not hurt anything.
Cutting thru 1" wood at the back of the sink (molded-in and not removable) is going to require one of those new-fangled oscillating tools, hopefully small enough to fit back there but likely won't have a cutting blade quite deep enough to cut 1" to the Corian. So it will be a PIA and require several passes, wood chisels, and curse words before the crap is cleaned away.
This faucet has Moen's "Hydrolock" mechanism at 3 locations, and for two of them when I pulled them off a washer and another ring stayed on the copper. I hope these go back together without leaking!!!
This 1/2 hour Disposal replacement job has turned into a two day, three trip affair fast. Oh, wait, it's not even close to being done yet!